The oxygen consumption rate (OCR) of cells is an important indicator of normal cellular function. It is used as a parameter to study mitochondrial function as well as a marker of factors triggering the switch from healthy oxidative phosphorylation to aerobic glycolysis in cancer cells. Oxygen consumption is traditionally measured by a cumbersome oxygen electrode, a specialized piece of equipment that typically yields low sample throughput. The phosphorescent oxygen probe, MitoXpress® Xtra, developed by Luxcel Biosciences offers a novel method for analyzing oxygen consumption in whole cells. Cayman’s cell-based Oxygen Consumption Rate Assay Kit (MitoXpress® Xtra HS Method) utilizes this newly developed phosphorescent oxygen probe to measure oxygen consumption rate in living cells. Antimycin A, an inhibitor of the mitochondrial electron transport chain, is included to be used as a positive control. Glucose oxidase is also included in the kit to be used as a reference for oxygen depletion. The kit is easy to use and can be easily adapted to high throughput screening for compounds which modulate oxygen consumption rate.